YTHDF2编码mRNA甲基化组调控髓系抑制细胞功能及肝脏自身免疫微环境的机制研究

Functional myeloid-derived suppressor cells(MDSC) accumulate in hepatic autoimmune microenvironment of primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH)，and MDSC serve as negative regulators of excessive T-cell responses. Thus, modulation of the MDSC population may be a promising immunotherapy strategy in autoimmune liver diseases（AILD）. Epigenetic modification of MDSC tend to be a potential tool to achieve this goal. Of note, recent studies highlight functional importance of mRNA m6A methylation in post-transcriptional modifications of gene and biological behaviors of cell. YTHDF2 is the crucial reader to recognize the m6A group and regulate both mRNA stability and localization. As indicated in our preliminary work, the number of CD11b+Ly6ChiLy6G- MDSC from bone marrow and liver were markedly increased in Ythdf2Δ249 mice compared to wild type control；moreover, knocking down of YTHDF2 in mice drove the expansion of MDSC from bone marrow cells in vitro. We hypothesize that YTHDF2 may serve as an immune checkpoint in the fate of MDSC population. In the present study, we aim to seek functional characteristic of mRNA-m6A modifications in MDSC and explore immunotherapeutic potential of YTHDF2-m6A-mRNA axis in AILD. Our study may elucidate a brand new epigenetic modification pathway of MDSC and provide the molecular target and insight to the precision medicine based immunotherapy for AILD.

原发性胆汁性胆管炎（PBC）、自身免疫性肝炎（AIH）等肝脏自身免疫微环境中可大量聚集功能性MDSC。MDSC谱系表观遗传调控或可成为治疗自身免疫性肝病（AILD）的突破点。以m6A修饰为特征的mRNA甲基化对基因的转录后调控及细胞的生物学行为意义重大。YTHDF2是识别和解析m6A甲基化密码的关键因子。我们发现，YTHDF2功能缺陷小鼠骨髓和肝脏中CD11b+Ly6ChiLy6G- MDSC的数量较野性型小鼠相比明显增加。 YTHDF2功能缺陷时骨髓细胞体外诱导MDSC的效率明显增加，提示YTHDF2可能是调控MDSC谱系的关键节点。本项目将以“YTHDF2-m6A-mRNA”表观轴为中心，分析MDSC内部mRNA-m6A修饰特征，并探讨其对AILD的免疫调控作用。本项目有助于为MDSC调控探索一条全新的表观信号道路，为AILD的表观免疫靶向治疗提供精准的理论依据。

原发性胆汁性胆管炎（PBC）、自身免疫性肝炎（AIH）、IgG4相关性胆管炎(IgG4-SC)等肝脏自身免疫微环境中可大量聚集功能性MDSC。MDSC谱系表观遗传调控或可成为治疗自身免疫性肝病（AILD）的突破点。首先PBC患者外周血和肝内均出现单核型MDSCs的明显积聚，且 MDSCs具有强大的免疫抑制功能。1.在PBC患者肝内受伤的小胆管可高表达CCN1，CCN1通过与MDSCs表面的整合素受体integrinαMβ2结合，促进STAT3的磷酸化，从而促进MDSCs扩增。同时CCN1还可诱导MDSCs高表达iNOS, 抑制T细胞的增殖。CCN1对功能性MDSCs的调控作用具有潜在的免疫治疗价值。2.接着，我们发现IgG4-SC患者肝内和外周血同样也出现单核型MDSCs的大量聚集，且这群MDSCs高表达RANK。RANKL可通过RANKL/RANK/NFkB途径诱导MDSCs的活化和扩增。RANKL活化后的MDSCs可有效抑制T细胞的增殖和诱导Th2分化。深入对RANKL/RANK轴调控MDSCs的相关研究，有望为日后开发 IgG4-SC生物免疫治疗打下坚实基础。3.我们进一步发现AIH患者外周血和肝内均出现单核型MDSCs的明显积聚。高表达MDSCs的AIH患者，免疫抑制治疗应答较佳。综上，功能性MDSCs是维持AILD患者肝内免疫稳态的重要负发挥机制，可抑制过度活化的T 细胞介导炎症反应。我们接下来以“YTHDF2-m6A-mRNA”表观轴为中心，分析MDSC内部mRNA-m6A修饰特征。我们利用YTHDF2功能缺陷小鼠和YTHDF2髓系细胞条件性敲除小鼠，发现YTHDF2在抑制MDSCs数量和扩增中发挥重要作用。通过多组学MeRIPseq、RNAseq和RIPseq相结合，探索YTHDF2调控MDSC谱系及功能的相关表观分子机制，为AILD的表观免疫靶向治疗提供精准的理论依据。